Water- or solvent-containing multicomponent systems, such as solutions, emulsions or suspensions, are frequently adjusted to higher viscosities or thickened for economical or performance reasons, or for stability reasons. Thus, for example, by increasing the viscosity of the external or internal phase of emulsions or suspensions, it is possible to significantly prolong the time before the components of such a system separate, which is evident from an extension of the shelf life. For many products, increasing the viscosity also improves their ability to be spread uniformly, in particular on uneven surfaces. This is true in particular for skincare compositions and pharmaceutical ointments on the skin. In the case of many industrial products, such as wallpaper stripping agents, paint strippers or aircraft de-icers, the increased viscosity prevents premature run-off from the surface to be treated. The more uniform distribution and extended contact time thus increase the effectiveness. As well as the performance advantages mentioned, the high viscosity of such preparations also offers further advantages during the preparation, packaging, containerizing and storage, as well as during transportation, the thickening of acidic media being of particular importance here from a safety viewpoint. In general, the rheological properties during the preparation and/or formulation of cosmetic, pharmaceutical or industrial preparations are a decisive criterion for the use of these products in practice. Even when used in extremely small amounts, the thickeners employed should lead to adequate thickening. However, the color and principal properties of the medium to be thickened should not be changed.
To adjust the rheological properties of aqueous or solvent-containing systems, emulsions, suspensions, a large number of different systems are given in the specialist literature. Known examples are cellulose ethers and other cellulose derivatives (e.g. carboxymethylcellulose, hydroxyethylcellulose), gelatin, starch and starch derivatives, sodium alginates, fatty acid polyethylene glycol esters, agar agar, tragacanth or dextrins. The synthetic polymers used are various materials, such as e.g. polyvinyl alcohols, polyacrylamides, polyacrylic acid and various salts of polyacrylic acid, polyvinylpyrrolidone, polyvinyl methyl ether, polyethylene oxides, copolymers of maleic anhydride and vinyl methyl ether, and various mixtures and copolymers of the compounds given above.
However, said compounds exhibit diverse disadvantages upon use. Thus, for example, the cellulose derivatives and, generally, the materials based on natural raw materials and the formulations resulting therefrom are very susceptible to bacteria. From an applications-related viewpoint, they are mostly noticeable from the formation of unpleasant “stringing” gels. Fatty acid polyethylene glycol esters tend toward hydrolysis in the presence of water, and the insoluble fatty acids which form in the process cause undesired clouding. Thickeners of natural origin (e.g. agar agar or tragacanth) have a composition which varies considerably depending on their origin.
EP-A-0 816 403 and WO 98/00094 describe crosslinked homopolymers of 2-acrylamido-2-methylpropanesulfonates and the use thereof as thickeners. EP-A-0 510 246 describes crosslinked copolymers of N-vinylcarboxamides and unsaturated alkylamides substituted by a sulfonate group, which are likewise suitable as thickeners. U.S. Pat. No. 5,080,809 describes non-crosslinked copolymers of N-vinylpyrrolidone and 2-acrylamido-2-methylpropanesulfonate. DE 199 05 639.0 describes crosslinked polymers of noncyclic N-vinylcarboxamides and acrylamidoalkylsulfonic acids.